The synthesis and characterization of homopolynucleotide sequences, particularly polyadenylic acid sequences is being investigated in cultured HeLa cells to develop the basic properties of these sequences and to use them to study the metabolism of the heterogeneous RNA of the nucleus and the messenger RNA of the cytoplasm. The ultimate goal of the project is to discover the function of these sequences, as well as the mechanism of their biosynthesis. A detailed study of a highly purified poly A polymerase from calf thymus nuclei is in progress to establish the mechanism of this reaction and the sites of specificity for the polynucleotide primer required for poly A synthesis. Other homopolynucleotide sequences are being investigated in the RNA of cultured cells. A technique for trapping large homopolynucleotides in polyacrylamide gels has been developed which permits a specific binding and elution of the complementary homopolynucleotide. Small amounts of polyuridylic acid sequences isolated in this way from HeLa cell RNA are being characterized.